Influence of gonadotropin treatment after insemination on dairy cows to maintain pregnancy, and milk progesterone concentration

The aim of the study is to evaluate the possibility of maintenance of cow pregnancy applying GnRH treatment after AI. The experiment was carried out on Lithuanian black-white lactating dairy cows on 90–100 DM. Were selected 45 cows on their 2nd and 3rd lactation with milk yield of 8.500–9.000 kg. The cows with 16 mm or greater (n=26) CL in ovaries were selected for the experiment. All cows were given the injections of dinoprost solution 25 μg. AI was performed on the cows (n=20) that showed oestrus. The first group (experimental) of cows (n=10) were repeatedly given the injections of gonadorelin 100 µg im on the 7th day after AI. The second group (control) of cows (n=10) were given the injections of 0.9% saline solution on the 7th day after AI. The ultrasound measurement was performed to determine the size of ovaries, and CL’s. Concentration of P4 were detected in milk samples. Ultrasound testing as well as milk P4 determination were carried out 4 times in total, every 7 days starting on the day of AI. After 7 days following the injection of GnRH, and positive increase of the number of cows with accessory CL by 56% was determined, comparing with the second (control) group. The tendency of increasing size of CL in both groups after AI was noticed. The changes in the ovary size were similar in both groups. The average number of CL in the first group was by 36% (P<0.05) higher than in the second group (1.5 and 1.1). The change of P4 was similar in both groups. The number of pregnant cows in the first group was by 10% higher than in the second group.